Jscodeshift-rxjs-first-value-from NPM

jscodeshift-rxjs-first-value-from

This codemod automates the migration from RxJS’s deprecated .toPromise() method to firstValueFrom and lastValueFrom. Promises piped with take(1) or first() are replaced with firstValueFrom, while other cases default to lastValueFrom. Import statements are also updated to include the new functions and remove unused imports.

jscodeshift-rxjs-first-value-from

Installation

To install the codemod, you can use npm or yarn.

npm install --save-dev jscodeshift-rxjs-first-value-from
# or
yarn add --dev jscodeshift-rxjs-first-value-from

You'll also need jscodeshift, the framework that powers this codemod.

npm install -g jscodeshift

Usage

To run the codemod, use the jscodeshift CLI and specify the path to the files you want to transform.

jscodeshift -t ./node_modules/jscodeshift-rxjs-first-value-from/src/first-value-from.ts src

Options

You can pass options to the codemod via jscodeshift if needed. This example is minimal in options, but you can extend or customize the script based on your project requirements.

Examples

`toPromise` to `firstValueFrom`

When calling toPromise on a pipe containing take(1) or first() the codemod will replace it with firstValueFrom.

Before:

import { take, map } from "rxjs/operators";

const name = getUser().pipe(map((user) => user.name), take(1)).toPromise();

After running the codemod:

import { firstValueFrom } from "rxjs";
import { map } from "rxjs/operators";

const name = firstValueFrom(getUser().pipe(map((user) => user.name)));

`toPromise` to `lastValueFrom`

When calling toPromise on a pipe without take(1) or first() the codemod will replace it with lastValueFrom.

Before:

import { map } from "rxjs/operators";

const name = getUser().pipe(map((user) => user.name)).toPromise();

After running the codemod:

import { lastValueFrom } from "rxjs";
import { map } from "rxjs/operators";

const name = lastValueFrom(getUser().pipe(map((user) => user.name)));

`toPromise` with type argument

When calling toPromise with a type argument, the codemod will cast the observable to the specified type.

Before:

import { map } from "rxjs/operators";

const name = getUser().pipe(map((user) => user.name)).toPromise<string>();

After running the codemod:

import { lastValueFrom } from "rxjs";
import { map } from "rxjs/operators";

const name = lastValueFrom(getUser().pipe(map((user) => user.name)) as Observable<string>);

`subscribe` to `firstValueFrom`

When calling subscribe on an observable with a single value, the codemod will replace it with firstValueFrom.

Before:

import { map } from "rxjs/operators";

getUser().pipe(map((user) => user.name), take(1)).subscribe((name) => console.log(name));

After running the codemod:

import { firstValueFrom } from "rxjs";
import { map } from "rxjs/operators";

firstValueFrom(getUser().pipe(map((user) => user.name))).then((name) => console.log(name));